Flopper Stopper

[Flossdog]

I am just about to start constructing a flopper stopper and the traditional shape is triangular. I am thinking of making a circular one as it is easier to stow. A triangular one of 1m sides would only need to be a circular one of 0.8m diameter to be the same surface area. But would it work as well? Does anyone have any thoughts or practical experience?

 

[macd]

I've used a drogue-type flopper stopper quite regularly, Very effective (in swell: the shorter the wavetrain, the less well it worked), but it needed a hefty pile of chain hanging off it to re-fill between rolls. This was first worked out from scratch in a very rolly anchorage in St Kilda. The effect was truly miraculous: it went from literally dipping the gunwhales underwater to a serene night's sleep.

I've had rigid triangular ones recommended and seen them in action. The absolute key is having a substantial weight at one corner - so that, after being lifted by a roll, the board dives quickly again ready for the next wave. This is absolutely key. But, since the weight's effect is so focussed (compared to a drogue) it needs be very much less. A clever and practical person thought that up.

No reason a circular board can't dive if weighted at one edge, but perhaps less effectively than a triangular one.

(Rythmic rolling in swell is somewhat akin to racing motorcycles going wild when steering dampers pack in. Once initiated, the forces involved are huge; but the initiation forces themselves are slight, so really quite modest counter-forces can constrain them. At least, that's how it feels.)

P.S. If you want to reduce rolling with (smallish) shorter waves, an easily deployable kedge is your best friend. Just align the boat perpendicular to the wave direction. Drop the kedge first, motor forward into the chop, drop the bower, then haul yourself back somewhere between the two.

 

[richardabeattie]

No perhaps about it - a triangle would have sides longer than the diameter of a circle of equal area and so the weight at one corner would have far more leverage.

 

[alant]

I am just about to start constructing a flopper stopper and the traditional shape is triangular. I am thinking of making a circular one as it is easier to stow. A triangular one of 1m sides would only need to be a circular one of 0.8m diameter to be the same surface area. But would it work as well? Does anyone have any thoughts or practical experience?

Get an old car tyre & drill some fixings into it.

 

[RupertW]

Angling the boat is our solution so far, but instead of a kedge we angle to boat with a line from the chain to the stern and adjust the bridle until the angle is right - but haven't yet had to do that at more than about 40 degrees to the wind. It also virtually stops the boat veering about. But in a strong wind I'd be less happy and a kedge would be better, I think.

 

[vyv_cox]

Some thoughts on the matter. A large flopper stopper will be less effective than a small one because on the inactive down stroke the weighted corner has to cover a large distance. However a small FS may be too small to have any worthwhile effect. The answer could ne have multiple small ones but this could be cumbersome. A man I know has a US made one rather like a Venetian blind, which he tells me works very well, keeping the boat almost stationary.

 

[Poey50]

I've just finished making one for my wife for Christmas (she's a lucky lucky woman) using some guidance on sizes from this article.
http://www.faymarine.com/Pauls Information Site/Flopper Stopper.htm

 

[RichardS]

Does anyone have any thoughts or practical experience?

Bolt on a second hull?

Richard

 

[RupertW]

Bolt on a second hull?

Richard

I can tell you that a 3m rib attached by two stout wooden posts to a 12m monohull stops the rolling almost completely. Only downsides compared to a catamaran are the reduced accommodation, massive sound of rib smacking the water echoing every 5 seconds across the anchorage and that even if you source your stout posts from a reputable Greek beach they still snap. Setting it all up was still the best post beer afternoon I'd had in ages.

 

[Flossdog]

Thanks for your posts Guys, will go for the triangular one I think. I've got a couple of old dive weights which will be ideal for the weights. Will be off to Lundy first thing next season as this will be quite a test!

 

[smithy]

Thanks for your posts Guys, will go for the triangular one I think. I've got a couple of old dive weights which will be ideal for the weights. Will be off to Lundy first thing next season as this will be quite a test!

Be sure and report back after testing.

 

[Graham_Wright]

Would a sheet hinged across the middle and (somehow) sprung to keep it open work? Maybe the support lines could connect to the hinge line as well as the extremities suitably sized lengthwise. It would perhaps be easier to stow below.

 

[rogerthebodger]

Would a sheet hinged across the middle and (somehow) sprung to keep it open work? Maybe the support lines could connect to the hinge line as well as the extremities suitably sized lengthwise. It would perhaps be easier to stow below.

This is the type with a hinge in the middle.

This was posted a while ago

http://www.ybw.com/forums/showthread.php?165909-Flopper-Stoppers

All kinds of different designs

https://www.google.co.za/search?q=f...VFDsAKHaFtC20QsAQIOA&biw=1920&bih=949#imgrc=_

 

[Flossdog]

Looks interesting but if the simple triangle of ply works well, why complicate the issue? Will report back when tried out.

 

[Little Dorrit]

This looks like one of those things that could be completely 'over-engineered' as we are now seeing! IMHO the simpler the better a triangular pieces of wood as already suggested would be my preference.

 

[Graham_Wright]

Looks interesting but if the simple triangle of ply works well, why complicate the issue? Will report back when tried out.

Stows more easily?

 

[Poey50]

Looks interesting but if the simple triangle of ply works well, why complicate the issue? Will report back when tried out.

People making them out of ply seem to use a central weight to sink the unit as a whole plus another weight on one corner. So it's possibly less complicated to use material that sinks. Mine is 6mm aluminium sheet with a panel edging strip epoxied on to protect the grp when deploying.

 

[KellysEye]

We used a bucket tied to the end of a raised boom and then lowered into the water. Seemed to work OK.

 

[Martin&Rene]

I made an equilateral triangular one out of 12mm ply with old prop anodes as weights. On the one time I used it hung of the end of the boom, you could see it dive neatly, but that meant the other two support lines were slack and so the boat needed to start rolling back up again before they tightened and the system became effective in slowing down the roll. Conclusion, the board only weights 4.5kg and is too light. The winter task is to find some more weight. I think the slanting diving effect is a second order effect and the weight of the unit is key.

Taking it too the limit, I think one made out of 2cm steel would sink fast enough, even when held horizontally

 

[Poey50]

Taking it too the limit, I think one made out of 2cm steel would sink fast enough, even when held horizontally

Someone may come along with some maths but my intuitive sense of this is that a diving corner will get the flopper lower more quickly than a heavier horizontal plate.